perl-module exports src_unpack() which actually introduces anything only in EAPI<2. Thus, exporting that function in EAPI>=2 only confuses developers, especially if the module is inherited indirectly (i.e. through perl-app) along with actual module exporting src_unpack() (like a VCS eclass). Considering that removing the export in EAPIs 2..4 could break compat, I suggest removing the export in EAPI 5. The one particular ebuild which was broken by that is mail-mta/qpsmtpd-9999; though I'm not sure when did the breakage occur.
This is fixed from EAPI=6 on.